One of the widespread, proven principles for increasing the economic efficiency of the chip-forming machining of workpieces is the consecutive performance of various machining operations in a single work set-up. Examples of this are, amongst others, automatic lathes and production centers. With a number of different cutting tools on one or several different machining units, all workpiece outer surfaces are machined that are accessible for machining in the relevant work set-up. Measuring operations on the workpiece surface are also included in the automatic process sequence. A multifunctional production center can substitute for a number of machines with different functions and machining techniques such as turning, milling, drilling, grinding and measuring.
The limits lie on the one hand in the machinery costs, which increase with the degree of outfitting, i.e. the number of machining units, NC axes etc., and on the other hand in the time expenditure for setting the machining process. The setting work is chiefly a substantial expense factor in the case of machining medium sized and small series, where the machine is reset frequently.
An example of multifunctional workpiece machining in the field of gear tooth and thread grinding is described in DE 196 25 520. In the first machining operation the teeth of a precut and hardened gear are ground by means of a grinding worm arranged on a first machining unit; in the second honed by means of a honing gear arranged on a second machining unit. By means of a measuring unit the workpiece is centralized prior to the machining of the tooth flanks; i.e. the workpiece teeth are aligned to coincide with the threads of the grinding worm. On this machine however, due to its manner of construction, only gears can be machined. Moreover the machining techniques employed here, those of continuous profile grinding and generation honing, demand workpiece specific dressing tools for the grinding worm and honing stone. The resulting relatively long setting and re-setting times mean that in spite of the high productivity, the machine is not economically suitable for small series. The number of machining operations in a single work set-up is restricted to two.
On another machine found on the market, the precut teeth of a hardened gear are rough ground in the first operation by the continuous generation grinding method at a high material removal rate, and in the second operation the exact tooth flank profile is produced by index profile grinding. Due to the style of construction of the machine, this solution too is only suitable for machining gears. And here too the number of machining operations in the one work set-up is limited to two.
Universal solutions for multifunctional machining, such as those afforded by modern production centers for broad spectrums of round or cubic workpieces, for example, are unknown in the field of gear tooth and thread grinding.